Annulus

Part of speech: noun

Pronunciation: /ˈænjʊləs/

Definitions

1. A ring-shaped object or structure, especially one formed between two concentric circles
2. A circular band or structure, particularly one situated between two different circular areas or surfaces
3. A ring-like formation that typically exists between two concentric circles or layers

Etymology: The most surprising thing about "annulus" is how little it changed on its way into English: it is a Latin word for a finger ring, borrowed largely intact. The Latin "anulus" was itself built from a root meaning "ring," with "-ulus" added as a diminutive ending, so the word was essentially "little ring" from the start. Its earlier form was spelled with a doubled "n" in medieval Latin, a misspelling of the classical form that the English word inherited. The word's modern sense of a ring-shaped region, rather than a piece of jewellery, came from the broader Latin usage of the original. Today it names everything from the flat band between two concentric circles in geometry to the ring of tissue around a heart valve or the solar ring visible during an annular eclipse. Its plural, "annuli," was also borrowed directly from medieval Latin, which is why it keeps its Latin ending instead of taking an English "-es."

Synonyms: ring, circle